1. Field of the Invention
This invention relates generally to a drive wheel system for industrial trucks that can be rotated around a vertical axis and includes a hub carrier, a hub mounted on the hub carrier which supports a driven wheel, and an electric travel motor.
2. Description of the Currently Available Technology
A known drive wheel system is described in GB 1 481 558. This drive wheel system has a travel motor that is a conventional radial field direct-current motor, e.g., a bar-wound armature motor, and is accordingly quite large. To reduce to a minimum the space required for construction, the travel motor is located radially inside the drive wheel. The housing of the travel motor serves as the hub carrier. Such a drive wheel system is used, for example, on a lift truck pulled by a tow bar or on a warehouse lift truck.
It is an object of the invention to provide a compact drive wheel system using means that are different from those in the known drive wheel systems.
The invention teaches that the drive motor of the drive wheel system of the invention is a disc armature motor. Disc armature motors require significantly less installation space than the radial field motors used in the known drive wheel systems, so that a designer has the maximum degree of freedom in the design and realization of the drive wheel system.
Downstream of the drive wheel system, there is advantageously a travel gearbox. This configuration makes it possible to keep the size of the travel motor small. To achieve particularly space-saving dimensions, the invention teaches that the travel motor, the hub with the wheel and the travel gearbox, if present, viewed in section along an axis of rotation of the wheel, are located within an envelope circle, the diameter of which approximately equals an outside diameter of the drive wheel system. Even when a wheel with only a small outside diameter is used, the envelope circle is not exceeded on account of the realization of the drive wheel system with a disc armature motor, in accordance with the invention.
In one advantageous refinement of the invention, the travel gearbox is realized in the form of a planetary gear train. A planetary gear train makes possible a large gear reduction while retaining a compact size.
A drive shaft of the travel motor is advantageously non-rotationally connected to a sun wheel of a first stage of the travel gearbox. A web of a second stage of the travel gearbox is non-rotationally connected with the hub carrier or is formed on the hub carrier. A ring gear of the second stage of the travel gearbox is connected with the hub.
If the wheel is located axially between the travel motor and the travel gearbox, both the travel motor and the travel gearbox are easily accessible. This is advantageous in particular during the assembly and installation of the drive wheel system of the invention.
With regard to the load-carrying capacity of the wheel bearing and the requirement for a small installation space, it is advantageous if the hub is mounted by means of at least two tapered roller bearings that are oriented at least-approximately symmetrically to the vertical axis.
In one favorable realization of the invention, a braking device can be provided that is located radially inside the mounting of the hub and axially between the travel motor and the travel gearbox.
The drive wheel system of the invention has advantages with regard to low maintenance requirements or no maintenance requirements at all if the braking device is realized in the form of a wet-running spring-loaded multi-disc brake.
On tow bar-guided industrial trucks in which the brake must engage due to technical requirements when the tow bar comes detached, it is favorable if the braking device is released by means of a mechanically actuated linkage. This linkage is effectively connected with the tow bar, which can move up and down.
In an additional configuration of the invention, however, it is also possible to realize the braking device so that it can be actuated, and in particular released, electromagnetically.
Finally, as described by an additional advantageous configuration of the invention, the braking device that can be actuated electromagnetically can also be actuated, and in particular released, hydraulically. The hydraulic actuation is then appropriately used in conjunction with a use of the braking device as an operating brake, while the electromagnetically acting actuation device is used to release the parking brake.
In one constructively favorable embodiment of the invention, the braking device has a first braking piston and a second braking piston. The first braking piston is spring-loaded in the direction of the closed position of the braking device, and in the closed position is in contact with the second braking piston. Axially between the two brake pistons, there is also a brake pressure chamber that is connected to a brake pressure channel in the hub carrier. In the open position of the braking device, the second brake piston can be moved by the braking pressure toward the closed position of the braking device.
In an additional advantageous realization of the drive wheel system of the invention, the braking device can be actuated, in particular released, by a hydraulic transmission device. In principle, this device is a xe2x80x9chydraulic linkagexe2x80x9d.
The transmission device appropriately has a master piston that is located in a master cylinder which is hydraulically connected to a slave cylinder. In the slave cylinder, there is a slave piston that can be released by a spring-loaded brake.
For industrial trucks that are not steered by a tow bar but by a handwheel, for example, the invention teaches that it is advantageous if there is a steering drive with a steering motor or with a steering motor and a downstream or secondary steering gearbox. The steering drive is directly connected with the drive wheel system and has a rotational mounting of the drive wheel system integrated into the steering motor or into the steering gearbox. Compared to known steering drives, which consist of a steering motor with a downstream or secondary gearbox and a chain drive that rotates the drive wheel system, the construction of the invention is significantly more compact.
The steering motor is appropriately realized in the form of a disc armature electric motor and the steering gearbox in the form of a planetary gear train. The base plate of an industrial truck provided with such a drive wheel system can thereby be very low or, conversely, while maintaining the conventional distance between the floor and the base plate, the wheel diameter of the drive wheel system can be increased so that there is more space available for the components of the drive wheel system and/or the industrial truck. Thus, the drive wheel system can carry a heavier load.
To achieve the greatest possible reduction between the speed of the steering motor and the rotational speed of the drive wheel system, the invention teaches that the steering gearbox is a Wolfrom gearbox (a special type of planetary gear train). A drive shaft of the steering motor is non-rotationally connected with a sun wheel of the steering gearbox. There are preferably two ring gears, axially one next to the other, with different numbers of teeth. The first ring gear is non-rotatably mounted and the second, rotating ring gear represents the drive element of the steering drive.
If the rotationally mounted ring gear of the steering gearbox is non-rotationally connected with the hub carrier and is mounted so that it rotates together with the hub carrier in a mounting on which the first ring gear is fastened or molded, the result is a simple integration of the rotational mounting of the drive wheel system in the steering gearbox of the steering drive.
To achieve a direct connection of the steering motor to the drive wheel system, the steering motor is advantageously fastened to the first ring gear. The drive wheel system of the invention is self-contained, compact and steerable, and can be installed and removed as a unit.